Color and/or effect coating systems on motor vehicle bodies, especially automobile bodies, nowadays consist preferably of a number of coats which are applied over one another and have different properties.
For example, an electrodeposition coat (EDC) as primer, a surfacer coat or antistonechip primer, a basecoat, and a clearcoat are applied in succession to a substrate. In this system, the EDC serves in particular to protect the metal panel against corrosion. In the art it is often also referred to as the primer. The surfacer coat serves to cover unevennesses in the substrate and because of its elasticity it imparts stonechip resistance. If appropriate, the surfacer coat may also act to reinforce the hiding power and to deepen the shade of the coating system. The basecoat controls the colors and/or the optical effects. The cleatcoat is used to intensify the optical effects and to protect the coating system against mechanical and chemical damage. Basecoat and clearcoat are often also referred to collectively as topcoat. For further details, reference is made to Römpp Lexikon Lacke und Druckfarben, George Thieme Verlag, Stuttgart, New York, 1998, pages 49 and 51, “Automotive Finishes”.
A disadvantage is that the application of these color and/or effect coating systems frequently takes place in four separate steps, between each of which it is necessary to flash off the coating and may also be necessary to bake the coating, which is time-consuming, labor-intensive, and leads to increased energy and equipment costs. A further disadvantage is the environmental burden when using solventborne coating materials.
It is therefore fundamentally desirable to reduce the number of application steps and thus the number of coats. However, this entails other disadvantages, such as, for instance, inadequate stonechip resistance, coloring and/or an optical effect which fail to satisfy the requirements, or deficient chemical resistance and weathering stability of the coating systems in question.
An equally important objective is to reduce significantly, or even totally, the amount of organic solvents emitted in the coating operation. Indeed, appropriate coating materials, such as EDC, aqueous surfacers, aqueous basecoats or aqueous clearcoats, powder coating materials or powder slurry clearcoats, are available. To use them conjointly to produce a color and/or effect coating system requires, however, that their properties be matched to one another with great precision in order to avoid, for example, the breakdown of the uncured coats when employing wet-on-wet techniques and/or to prevent cracking, popping, and/or coat delamination. Furthermore, especially in the case of the aqueous basecoats, it is still always necessary to use a comparatively large amount of organic cosolvents in order to disperse the pigments stably and to ensure effective leveling of the applied coats.
The production of coats with different functions from aqueous dispersions of powder coating materials, also referred to by those in the art as powder slurries, is known.
For instance, Japanese Patent Application JP 53 109 540 A1 (Derwent Abstract 78800A/44) discloses a coating system comprising a basecoat which is from 10 to 45 μm thick and is prepared from a pigmented powder slurry, of which no further details are given, and a clearcoat which is from 30 to 70 μm thick. Whether the basecoat also functions as a surfacer or antistonechip primer is not specified.
German Laid-Open Specification DE 27 10 421 A1 discloses a powder slurry which comprises metal-effect pigments and is based on amine-neutralized acrylate copolymers and melamine resins or on polyesters and epoxy resins. The preparation of the pigmented powder slurries, however, requires that the water-soluble amine-neutralized starting materials be neutralized with hydrochloric acid. This may, however, permanently damage the metal-effect pigments. The known powder slurry gives smooth, glossy, metallic coatings. It is not said whether this slurry in addition may also take over the function of surfacer coats in coating systems.
Japanese Patent Application JP 02 014 776 A2 discloses a multicoat system, comprising basecoat and clearcoat, whose basecoat is prepared from a pigmented powder slurry based on hydroxyl-containing acrylate copolymers and blocked polyisocyanates. Here again, nothing is said as to whether the basecoat may also take over the function of a surfacer coat or antistonechip primer.
U.S. patent application Ser. No. 5,379,947 A1 discloses cosolvent-free pigmented and unpigmented powder slurries based, for example, on hydroxyl-containing acrylate copolymers and blocked polyisocyanates or glycidyl-containing acrylate copolymers and 1,12-dodecanedicarboxylic acid. The pigmented powder slurries can be used either to prepare primers, i.e., surfacer coats or antistonechip primers, or to prepare basecoats. Whether they are suitable for the production of coats able to fulfill both functions in a color and/or effect coating system is not stated
It is an object of the present invention to provide a new color and/or effect coating system with a reduced number of coats which no longer has the disadvantages of the prior art but instead can be produced in fewer process steps than possible to date and without the use of cosolvents, the intention being that the good performance properties of the known coating systems in all their functions should be retained completely or even exceeded.